1. Field of the Disclosure
This disclosure relates generally to devices for administering anesthesia to patients and, more particularly, to the long term delivery of inhaled anesthetic agents to intubated patients undergoing ventilatory support outside of the perioperative environment; and devices for the delivery of said agents.
2. Description of the Related Art
Anesthesia using volatile anesthetic agents is commonplace. The properties of inhaled anesthetics are well known in the literature for their favorable properties, including rapid onset and recovery, controllability and a favorable safety profile. Such favorable properties more closely approximate an ‘ideal’ agent than common intravenously-delivered (IV) agents typically used in the intensive care unit (ICU) environment for patient sedation. To the present day, the use of volatile anesthetic agents has been (largely) limited to operating rooms (OR's) for procedures where the clinical objectives include rendering and maintaining unconsciousness, analgesia and amnesia.
A therapy of the present disclosure involves the use of these agents outside of the OR. Specifically, this disclosure includes a therapy in which the above clinical objectives are carried out outside the perioperative environment; such as in the ICU. The therapy of the present disclosure involves the use of primarily sub-maximum allowable concentration (sub-MAC) dosages of these agents over periods which can extend to multiple days in contrast to OR-based use of these agents in which patients are typically sedated at higher MAC concentrations and for shorter periods of time (hours). Additionally, the optimal volatile anesthetic agent for the therapy is described, and one embodiment of a hardware configuration suitable for implementation of this therapy is described in detail.
The origins of inhaled anesthetic agents can be traced back to the late 18th century when British clergyman, philosopher, and educator, Joseph Priestly, first identified the gas nitrous oxide. Priestly's prodigy, Humphrey Davy, later recognized the analgesic effects of nitrous oxide in the early 19th century. Early attempts at using anesthetic agents for pain-free surgery included the use of Diethyl Ether, Chloroform, and Nitrous Oxide and the origins of the practice of anesthesiology is typically traced to the 1840's when the first operation using such agents for the excision of a neck mass was performed at Massachusetts General Hospital by Dr. William Morton (although others claim to have used the agents earlier). The somewhat concurrent rise of the use of injectable local anesthetics traces back to the 1850's when morphine was first injected for treatment of painful neuralgias. The use of other injectable and IV agents followed including cocaine in the 1880's, and procaine in the early 1900's. The science of both inhaled and IV anesthetic compounds has, of course, progressed and today common inhaled agents include sevoflurane, isoflurane, and desflurane. Common IV anesthetics have progressed from chloral hydrate, to short acting barbiturates such as thiopental, to the common medications used today such as propofol, midazolam and dexmedatomidine.
To this day, the use of inhaled agents is generally limited to the operating room (OR), (although uses in MRI and Labor and Delivery settings are envisioned), and patients who have undergone surgical procedures are typically switched from inhaled agents in the OR to IV medications when moved (post-surgery) to the intensive care unit (ICU). All IV medications currently in use for sedation suffer from drawbacks including undesirable variability in patient wakeup time following discontinuation, and difficulty in clinical control of depth of sedation. Modern inhaled anesthetics such as desflurane, by contrast, are widely regarded as having rapid onset and recovery, and good controllability. Therefore, it is the intent of the therapy and system of this disclosure to extend the useful range of inhaled anesthetics beyond the operating room environment into the ICU environment for intubated, mechanically ventilated patient populations. Further, it is the intent of the present disclosure to extend the duration of therapy from hours, as is current practice in the OR, to potentially (multiple) days of therapy.
In order to achieve these goals, a hardware system will be described which integrates into existing technologies being used in the ICU environment for patient respiratory support. Specifically, the therapy of the present disclosure integrates with typical ICU ventilators, and as such provides inhaled agents to the patient concomitant with ventilator gas flow. The integration of the technology is not ventilator specific, meaning that it will integrate with any modern ICU ventilator. Further the technology is not mode specific and will work independent of ventilator mode and settings, ensuring broad functionality of the technology with modern ICU ventilators.
Prior art can be broadly classified as falling into three categories, first are patents related to technologies for anesthetic vapor delivery in an OR setting, second are patents on volatile anesthetic scavenging/reclamation as applied to the OR setting, and third are patents related to anesthetic reflector technologies for the on-airway conservation of anesthetic vapor for use outside the OR setting.
It is an object of the present disclosure to provide an anesthesia therapy and device which can be implemented using modern, microprocessor-based ICU ventilators. This objective being, in general, at odds with the plurality of art which seeks to provide such therapy in an OR setting. The difference in clinical setting may require different sedative regimens, as well as technology with notably different pneumatic and functional characteristics.